News of the Wild

Animal News

04-01-1997
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NWF Staff

Pollution's Hidden Toll on Native Plants

Nitrogen is an important plant nutrient, right? So when your car spews out nitrogen emissions into the environment and they settle onto the ground, are you enhancing plant growth? The answer may be yes, but, scientists are discovering, it's not the kind of growth that benefits native plants.

For 12 years, ecologists David A. Wedin of the University of Toronto and David Tilman of the University of Minnesota have applied nitrogen to 162 plots of native grasses at levels that approximate the amount of nitrogen that occurs in air-borne pollution from cars and power plants in the Northeast. Though plants need nitrogen to grow, the researchers found that the elevated nitrogen levels stimulated the growth of grasses imported from Europe while impairing the growth of native grasses.

This unusual situation apparently results from the way the two groups of plants use nutrients. Native grasses thrive in areas of relatively low nitrogen, while European interlopers imported for agricultural development need large doses of the nutrient. Once nitrogen increases in the soil, as when motor-vehicle pollution settles to the ground, nonnative plants take over. Subsequent changes in the soil also increase nitrogen pollution in water supplies. In addition, species diversity in affected areas declines.

The news represents another blow to the nation's grasslands, which have declined considerably. What's more, observes Wedin, the disruptions caused by air-borne nitrogen may not be restricted only to grasslands, since the same effect is likely in other plant communities.

Bird Breeding: It's All in the Head

When mating season rolls around, animals respond in various ways. Deer grow antlers for their annual rut. Bull elephants become belligerent. And some male birds put on their brightest feathers and grow bigger brains.

Yes, it's true: Their brains actually grow in size, according to recent research on canaries, eastern and spotted towhees and song sparrows.

"The changes are so extreme that you can see them [during dissection] with the naked eye," says Troy Smith, a University of Washington zoology graduate student who not long ago completed research on spotted towhees and song sparrows. Among his findings: Two parts of the brain associated with song production in the song sparrow triple in size during spring mating season. These differences in size may be the most dramatic examples of nerve growth in any adult animal, Smith says.

The change results from increased testosterone, which rises nearly 100-fold between October and late April, when the birds are issuing their mating calls. Smith also found that in the fall, the notes and trills of song sparrow songs are more variable than they are in the spring. However, the number of songs that song sparrows sing does not change with the seasons.

Gallons of freshwater one gallon of used motor oil can pollute: 1,000,000

Studies of streams in the Pacific Northwest are showing that clean streams alone will not maintain salmon and trout populations. The waters also must be cool--yet cool waters are hard to find in a region where logging and grazing have removed bank vegetation along many streams.

The Oregon Department of Environmental Quality recently classified more than 500 segments of Oregon rivers and streams as "water-quality limited" because of their high temperatures. Elevated water temperatures in summer can kill trout, salmon and the food they eat. "The fish are just barely surviving by seeking out cool water seeps on hot days," says Bob Beschta, an Oregon State University hydrologist who helped develop the state's current water-temperature standards. "High temperatures are sometimes lethal for fish."

The eastern end of the state is characterized by open country interspersed with forested lands. Prior to logging and grazing along rivers and streams, vegetation shaded the running waters. "Now, many of the riparian ecosystems are not intact," says Beschta. "The streamside vegetation is gone, channels are wider and shallower, with more sun hitting the water surface." Temperatures are high, and such conditions can be tough on the fish.

It amazes me that we still have salmon and trout in some of the places of the east side," says Beschta. "Ultimately they will be gone if we don't do something."

Out Foxing a Fish

In a rarely photographed scene on Alaska's Katmai Peninsula, a red fox finds a meal in a creature more often associated with bears than small canines: a silver salmon. When migrating chum and silver salmon become grounded in shallow tidal waters during their spring runs, foxes rush in to take advantage. A mature salmon is too heavy for a fox to lift, so the wily predator will pull the fish onto a sandbar, then kill it and break it into small pieces to carry back to the den.